Process for the application of solder on printed circuit boards and process for their placement in and removal from this device

ABSTRACT

Clamp-like guides are arranged in the interior of a soldering bath container at a distance from each other and distributed across the width of the soldering bath container. Each guide has two guide rods which are spaced from each other by a certain distance and which are connected with each other at their lower ends. The upper final sections of the guide rods project upward from a soldering bath and have deflections at their upper ends which form a narrowing therebetween. The final sections can be elastically deflectable and are supported by support springs. Above the guides, two blast nozzles extend across the width of the soldering bath container and direct hot air jets against the surfaces of printed circuit boards leaving the soldering bath. The width of the narrowing is somewhat larger than the thickness of the printed circuit boards. Several guiding points are formed across the width of the printed circuit board by the guides without necessitating a constant mechanical contact between the printed circuit board and the guide rods. Since the upper final sections of the guide rods can elastically yield when the printed circuit board abuts against the deflections, damage to the printed circuit board is avoided.

This is a division of application Ser. No. 300,971, filed Sept. 9, 1981now U.S. Pat. No. 4,414,914.

BACKGROUND OF THE INVENTION

The present invention relates to a process for the application of solderon printed circuit boards.

In the case of a known process of this type, a guiding system consistsof two vertical guiding rails each of which has a U-shaped guidingchannel (German Disclosure Publication 24 11 854). The printed circuitboards are guided in these guiding channels and also are held on twonarrow sides located opposite each other. The guiding rails extend fromthe soldering bath upward past blast nozzles from which emerge hot airjets which are directed against the surfaces of the printed circuitboards pulled out of the soldering bath. By means of these air jets,excessive solder is removed from the printed circuit board which passesby and, additionally, the solder is removed from passage holes in theprinted circuit boards. In order to be able to properly hold and guidethe printed circuit boards, particularly when they are exposed to thehot air jets, the width of the guiding channels is selected in such amanner that it corresponds approximately with the thickness of theprinted circuit boards.

This requires a very exacting and, therefore, complex positioning of theprinted circuit boards for their introduction into the guiding channels.Furthermore, printed circuit boards which are slightly curved can onlybe introduced with difficulty or not at all. Furthermore, an adjustmentor exchange of the guiding rails becomes necessary for the processing ofprinted circuit boards of different widths or thicknesses. Since theprinted circuit boards are softened in the hot solder bath, there isadditionally the danger of damaging the printed circuit boards, whichare not yet resistant to mechanical wear when leaving the solderingbath, owing to the heavy lateral guide.

SUMMARY OF THE INVENTION

It is the purpose of the present invention to avoid the aforementioneddisadvantages and thus to provide a process of the type mentioned abovewith which printed circuit boards of different widths and thicknessesand also printed circuit boards which are not exactly plane can beintroduced into a solding bath without the necessity of very exactpositioning and thus with a high operating speed, whereby the printedcircuit boards nevertheless are properly guided and held during theirmovement and are not exposed to the danger of being damaged.

This task is accomplished according to the invention by the provisionthat the printed circuit boards are not guided along two edges by tworows of guiding elements, but rather are guided across their entirewidth on both sides. Proper guiding is guaranteed by the thus resultingmultitude of guiding points without necessitating a constant mechanicalcontact between the printed circuit boards and the guiding elements.Moreover, the necessity of a very exact positioning of the printedcircuit boards, as is required for the introduction into guiding rails,is eliminated. Even slightly curved printed circuit boards can beintroduced and guided without any difficulty. The danger of damaging theprinted circuit boards is thus largely avoided. Furthermore, thenecessity of adjusting the guiding elements to different board widths orthicknesses is eliminated.

According to the invention, the placement of printed circuit boards inor for their removal from the device is characterized by the fact thatthe respective, vertically aligned printed circuit board is necessarilycentered vertically with respect to its plane relative to the guidingsystem in the soldering bath container during the placement or removalprocess. In this manner, a quick and exact placement or removal, of eachprinted circuit board into or from the device is guaranteed withoutrequiring a complex manipulation.

The centering of the printed circuit boards is appropriately effected bymeans of guiding elements which are preferably arranged between theopening in the casing cover and the blast nozzles.

It is particularly essential for the process according to the inventionthat the printed circuit board is guided and/or positioned withoutconstant mechanical contact. In this fashion, on the one hand, exactguiding and positioning of the respective printed circuit boards isguaranteed in the soldering bath and, on the other hand, the danger ofdamaging the printed circuit plates which are especially sensitive aftercoating is avoided.

Advantageously, the guiding and/or positioning of the printed circuitboard is effected without constant mechanical contact by means of aguiding system which has several guiding elements running essentiallyvertically and which are arranged in two rows opposite each other and inrows at a distance from each other distributed across the entire widthof the printed circuit boards introduced into the soldering bath.

The process according to the invention solves the especially criticalphase of the removal of the respective printed circuit board from thesoldering bath container in a technically advantageous manner. Thisphase is a critical one for two reasons. First of all, the carriermaterial of the printed circuit plates is softened owing to therelatively high temperature of the soldering bath so that the printedcircuit plates are particularly sensitive to being damaged when pulledout of the device, for example, by being bent or such. Secondly, the hotair jets, acting on both wide sides of the printed circuit board when itis pulled out, can cause vibrations of the printed circuit board bymeans of which the printed circuit board can abut against components ofthe device and damage to the printed circuit board can thus be caused.The respective printed circuit board can be subjected to vibrations bythe hot air jets because the blast nozzles are arranged staggered withrespect to each other in the vertical direction on opposite sides of thetransport path of the printed circuit boards. This staggering isnecessary since, if the blast nozzles were arranged directly oppositeeach other, they would essentially neutralize each other when blowingthrough the passage holes in the respective printed circuit board and,thus, the excessive solder would not be sufficiently removed from thepassage holes in the printed circuit boards.

The process according to the invention makes sure that, with the removalof the respective printed circuit plate, the latter is stabilizedrelative to the air jets acting upon the two wide sides of the printedcircuit board in a vertically staggered fashion. This stabilization isachieved by means of a number of elements which are arranged in two rowsopposite each other and in rows at a distance from each otherdistributed across the entire width of the printed circuit boardintroduced into the soldering bath and which extend from below as far aspossible into the space between the two blast nozzles. In this context,it is particularly expedient that the elements are designed verticallyin an elastic way relative to the respective wide sides of the printedcircuit board.

In the preferred embodiment of the invention, these elements are formedby the upper final sections of the guiding elements.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplified embodiment of the present invention will be explainedbelow in greater detail with reference to the accompanying drawings,wherein schematically:

FIG. 1 is a cross-section of a device for the tin-plating of printedcircuit boards according to the invention and

FIG. 2 is a longitudinal cross-section through the tin-plating devicealong the line II-II in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The structure and the mode of operation of the tin-plating device forprinted circuit boards now will be described on the basis of thedrawings. As employed below, the term "tin-plating" refers not only to alead-tin alloy, but also to any suitable solder of a different type.

The tin-plating device has a casing indicated by 1 which is closed onthe top by a cover 2. In this cover 2, there is a slot-like opening 3for the printed circuit boards.

A solder bath container 4 is arranged in the lower part 1a of the casing1 and is open towards the opening 3 and is closed off at the bottom by aperforated bottom 5. The interior of the solder bath container 4 is inconnection, through perforated bottom 5, with a distribution chamber 6which is provided on the bottom of the lower part 1a of the casing. Theactual solder bath 7 is in the solder bath container 4. A collectingchamber 8 is formed for the solder between the walls 4a of the solderbath container 4 and the walls 1b of the lower part 1a of the casing.The solder is transported from the distribution chamber 6 upward throughthe solder bath container 4 by means of a pump which is not shown. Thesolder flows subsequently into the collecting chamber 8 over the upperedges of the container walls 4a from where it enters again thedistribution chamber 6. The heating system required for the heating ofthe solder which is of an actually known design is not shown. While thepump is not operating, the level S of the solder bath is below the upperedge of the walls 4a of the solder bath container 4, it is shown in thedrawings.

Guides 9 are arranged in the interior of the solder bath container 4 ata distance from each other and distributed across the width of thesolder bath container 4, as can be seen from FIG. 2 in which a portionof the casing is not shown at the bottom and on the right side. Each ofthese guides 9 is formed by two rod-like guide elements 10 and 11 whichare spaced opposite each other at a certain distance from each other andwhich are connected to each other at their lower ends, as can beparticularly seen from FIG. 1. The thus clamp-like designed guides 9extend into the area of the perforated bottom 5 of the solder bathcontainer 4 and project above the solder bath level S. At the end oftheir upper final section 10a or 11a, respectively, the rod-like guideelements 10, 11 are provided with deflections 12 and 13, respectively.As is shown in FIG. 1, the deflection 12, 13 of each guide element 10,11 projects toward the opposite guide element 10 or 11, respectively, sothat there is provided a narrowing 14 of the space 15 between the twoguide elements 10, 11 by means of deflections 12, 13 of the guideelements 10, 11.

The upper final sections 10a, 11a of the guide elements 10 and 11,respectively, projecting upward out of the solder bath 7 can bespring-elastically spread apart and are, for this purpose, supported bystationary support springs 16 and 17, respectively. In the area of thesolder bath level S, mounting supports 18 and 19, respectively, areattached to the inner sides of the walls 4a opposite each other of thesolder bath container 4 in which the guides 9, i.e. the guide elements10 and 11, are held. Instead of a single munting support 18 or 19,respectively, for the guide elements 10 or 11, respectively, also aseparate mounting support can be provided for each guide element 10 or11 which is fastened to the container walls 4a. The mounting supports18, 19 are attached at such a level on the walls 4a that they slightlyproject above the solder level S when the pump is out of operation sothat the seat of the in mounting supports 18, 19 can be inspected time.Two blast nozzles 20 and 21 are arranged above the guides 9 and extendacross the entire width of the solder bath container 4 and form betweenthemselves an interspace 22 which is aligned with the narrowing 14.These blast nozzles 20, 21 are connected to a hot air source, such as isdescribed in greater detail, for example, in German DisclosurePublication 24 11 854. Two semi-circular tubs or troughs 32, 33 whichextend preferably across the entire width of the solder bath container 4and in which the excessive solder, as removed by the hot air jets, iscaught, are arranged in parallel to the two blast nozzles 20, 21. A wormgear, not shown, is arranged in each of the tubs 32, 33, by means ofwhich the excess solder is discharged laterally from the system beforesolidifying, preferably in a continuous manner. There are two guideelements 23 and 24 extending in parallel to each other above the twoblast nozzles 20, 21 and also extending across the width of the solderbath container 4 parallel to the blast nozzles 20, 21. Each of theseguide elements 23, 24 has a carrier rod 25 or 26, respectively, on whichguide disks 27 or 28, respectively, are positioned at a distance fromeach other (see especially FIG. 2). The guide disks 27, 28 can be madeso that they are spring-elastically deflectable. The guide elements 23,24 form between them an opening 29 which is aligned with the opening 3in the casing cover 2 and the space 22 between the blast nozzles 20, 21.

A printed circuit board 30 is shown by dot-dash lines and is held by aschematically indicated gripping device 31.

The operating method of the described tin-plating device is as follows.

The printed circuit board 30, which is seized in a known manner by thegripping device 31, is introduced into the device through the opening 3in the casing cover 2 and passes between the two guide elements ormembers 23 and 24. These guide elements 23, 24 have the task of guidingcurved printed circuit boards 30, without damaging them, past betweenand the blast nozzles 20, 21 to the guides 9. Subsequently, the printedcircuit board 30 passes through the narrowing 14 between the guideelements 10, 11, arranged opposite each other, into the space 15 betweenguide elements 10, 11. The width of narrowing 14 is somewhat larger thanthe thickness of the printed circuit board 30 so that the latter, if itis entirely planar, can be passed, without contact, between thedeflections 12, 13 of the guide elements 10 and 11. The upper finalsections 10a, 11a of the guide elements 10 and 11 are pushed apart bythe gripping device 31 and spring back again into their originalposition owing to their own elasticity and/or under the effect of thesupport springs 16, 17. When curved boards are introduced, the finalsections 10a, 11a can also be spread apart, which permits theintroduction even of curved boards without damaging these boards by theguide elements 10, 11.

After having passed the narrowing 14, the printed circuit board 30enters the space 15 between the guide elements 10, 11 which isconsiderably larger than the thickness of the printed circuit board 30.The solder is then applied on the printed circuit board 30 in the solderbath 7 in the known manner.

Since, as already mentioned, the guides 9 extend into the area of theperforated bottom 5, even curved boards are held by guides 9 essentiallyin the center of the solder bath container 4. Guides 9 thus prevent theprinted circuit boards 30 from coming into contact with the walls 4a ofthe solder bath container 4. As is shown in FIG. 1, the guide elements10 and 11 converge together towards the bottom whereby the space 15between these guide elements 10, 11 becomes correspondingly narrower.This measure contributes additionally to a proper positioning even ofcurved printed circuit boards 30 in the center of the solder bathcontainer 4.

After the tin-plating process is terminated, the printed circuit board30 is pulled out again from the solder bath 7 in the known manner. Bydoing so, it is moved through the narrowing 14 and between the blastnozzles 20 and 21. During this movement, hot air jets leaving the blastnozzles 20 and 21 act on both sides of the printed circuit board 30.Excess solder is removed by means of these hot air jets and solder inthe passage holes in the printed circuit board 30 is removed asdescribed in detail, for example, in German Disclosure Publication 24 11854. After the excess solder has been removed, the printed circuit board30 is led out of the device through the opening 29 and the casingopening 3.

Owing to the guide elements 10, 11 on both sides of the printed circuitboard 30 being formed in rows being arranged at a certain distance fromeach other and being distributed across the width of the printed circuitboard 30, several guide points are formed which guarantee sufficientguiding and positioning without a constant mechanical contact betweenthe printed circuit board 30 and the guide elements 10, 11. As hasalready been mentioned, the width of the narrowing 14 is somewhat largerthan the thickness of the printed circuit board 30 so that, as a rule,the guide elements 10, 11, i.e. their deflections 12, 13, do not rest onthe printed circuit board 30. Since the upper final sections 10a, 11a ofthe guide elements 10, 11 can be bent out in a spring-elastic manner,these final sections 10a, 11a can elastically turn away if the printedcircuit board 30 abuts against deflections 12, 13. The printed circuitboard 30 is exactly guided, on the one hand, and damage thereto by theguides 9 is avoided, on the other hand, since these guides 9 do notrepresent a solid mechanical resistance to the printed circuit board 30.

The distance between the guide elements 10, 11, arranged opposite eachother, becomes larger below the narrowing 14. This means that no contactnormally takes place below this narrowing 14 between the printed circuitboard 30 and the guide elements 10, 11. The printed circuit board 30thus is freely accessible on all sides in the solder bath 7 and is notcovered anywhere by the guides 9.

When pulling out the printed circuit board from the solder bathcontainer 4, the upper final sections 10a, 11a of the guide elements 10,11 act in a particularly advantageous manner as stabilizing elementswhich prevent vibration of the printed circuit board by the hot air jetsfrom the blast nozzles 20 and 21, arranged as shown in FIG. 1 to bevertically staggered with respect to each other, which would otherwisecause the printed circuit board, being particularly sensitive in theposition, to abut against components of the device and thus would leadto damage to the printed circuit board. For the purpose of the desiredstabilization of the respective printed circuit board when it is removedfrom the device, the upper final sections 10a, 11a of the guide elements10, 11 project as far as possible into the space 22 between the twoblast nozzles 20 and 21 which are somewhat staggered with respect toeach other in the vertical direction. Additionally, the upper finalsections 10a, 11a of the guide elements 10, 11 are designed to bespring-elastic in directions transverse to the wide sides of the passingprinted circuit boards so that the respective printed circuit board isstabilized by these means and damage to the printed circuit board, byabutting against the upper final sections 10a, 11a of the guide elements10, 11, is avoided. Finally, the width of the gap 14, between the upperfinal sections 10a, 11a of the guide elements 10, 11 or of thedeflections 12, 13, is determined or adjusted for the desiredstabilization of the printed circuit board to be removed from the solderbath.

Since the guides 9 act on the front and rear sides of the printedcircuit board 30 and the printed circuit board 30 need not, therefore,be guided at its edges, the necessity of an exact lateral positioning iseliminated and printed circuit boards 30 of different widths can beprocessed without requiring an adjustment of the guides 9.

It goes without saying that the described tin-plating device can bedesigned differently from what has been shown with regard to variousparts. Only a few of the possible variations are mentioned below. Thewidth of the gap between the deflections 12, 13, i.e. the width of thenarrowing 14, can be changed by modifying the force which is exerted onthe upper final sections 10a, 11a by the support springs 16, 17. Thiscan, for example, be achieved by using support springs 16, 17 withdifferent spring characteristics. If the upper final sections 10a, 11aof the guide elements 10, 11 have the necessary spring-elasticproperties, the support springs 16, 17 may be eliminated under certaincircumstances.

Owing to the fact that the guide elements 10, 11 positioned oppositeeach other in pairs and are connected with each other, a particularlyadvantageous design is obtained from the point of view of production,effect and maintenance. However, it is also possible not to connect thelower ends of the pairs of guide elements 10, 11 arranged opposite eachother, at their lower ends. Furthermore, the guide elements 10 can belaterally staggered vis-a-vis the guide elements 11 so that guideelements 10, 11 are no longer directly opposite each other relative tothe printed circuit board 30.

I claim:
 1. A process for applying solder to a printed circuit board, said process comprising:vertically downwardly introducing a printed circuit board through an open upper end of a solder bath container containing a solder bath, thereby applying solder to said printed circuit board, and then vertically upwardly withdrawing said printed circuit board from said solder bath through said open upper end of said solder bath container; and guiding said vertically downward and upward movements by loosely contacting only opposite sides of said printed circuit board and without contacting lateral edges thereof by means of a guide system, while simultaneously centering said printed circuit board, in opposite directions transverse to the vertical plane thereof, by means of said guide system.
 2. A process as claimed in claim 1, comprising providing said guide system as a plurality of generally vertically extending rod-shaped guide elements extending into said solder bath within said container, and arranging said guide elements in two parallel rows spaced from each other by a distance greater than the thickness of said printed circuit board, with each said row comprising plural said guide elements spaced from each other across the width of said container, and said centering comprises centering said printed circuit board between said two rows of guide elements.
 3. A process as claimed in claim 2, further comprising elastically biasing an upper portion of each said guide element in a direction toward the opposite said row of guide elements.
 4. A process as claimed in claim 1, further comprising directing gas jets against opposite sides of said printed circuit board during said vertically upward movement thereof, thereby removing excess solder from said printed circuit board.
 5. A process as claimed in claim 4, comprising vertically staggering said gas jets on one side of said printed circuit board with respect to said gas jets on the opposide side thereof. 